The invention relates to a novel type of plate exchanger. It also relates to heat-exchange plates allowing the production of such an exchanger.
Current heat exchangers are divided into two main categories, namely tube exchangers, whose design is already old, and plate exchangers, which are more recent and have the feature of being easy to disassemble and alter.
In general, exchangers with plates and joints consist of a stack of a defined number of ribbed plates, of the same type, which are clamped between two flanges, in particular using tie-rods. These plates have openings at their corners which, within the stack thus constituted, define respective supply and outlet channels for the heat-exchange fluids. A circulation network is defined between two consecutive plates by virtue of the ribs, of one of the fluids, for example the hot fluid, which transmits, through the two plates, heat to the other cold heat-exchange fluid which flows in the opposite direction between the two immediately consecutive plates.
Until now, these heat-exchange plates have been made of any deep-drawable metallic material, in particular stainless steel, titanium, etc., which can exhibit relatively good heat-exchange performances while being compact. Nevertheless, it has been designed to improve the heat exchange between two successive plates and therefore resort to a material having a greater capacity for ensuring heat exchange.
Among these various materials, there is one which is an especially good conductor of heat, namely graphite. Nevertheless, it has the great drawback of having relatively poor mechanical strength so that, until now, it has not been used for producing such plates.
It has now been proposed, in order to overcome this deficiency in mechanical properties, to mold ribbed plates from a resin of the PVDF type (polyvinylidene sulfide), or from a fluorinated polymer incorporating graphite particles (see for example EP-A-0,203,213). In addition to the requirement of a specific press for obtaining this molding, obtained in the case in point by pressing, the plates obtained do not exhibit a very significant improvement in heat exchange performance, considering the insufficiency of the concentration of the graphite particles in the composite material obtained.
It has also been proposed, for producing such plates, to incorporate expanded graphite within a carbon-carbon structure, the assembly thus produced then undergoing hot pressing, so as to obtain the desired profile for said plates. However, in addition to the difficulty relating to the pressing operation, it is observed that, despite the use of graphite, the heat-exchange performance remains unsatisfactory.